With regard to DPS, the rogues in my guild who know how to play pull really good DPS. As a pure DPS class though, I personally feel they are a little weak when compared to, say, hunters, who I've seen pull incredible DPS.

Utility:
Tanking:
Although this hasn't been required in WotLK, in BC there were a few fights (notably Reliquary of Souls) where dodge tanking was necessary. It's also useful for surviving an enrage with only a little health left - tank gets one shot, so step in and dodge tank 'till you too get 1 shot.
Threat:
Tricks of the Trade is a spell similar to Misdirection, in that it transfers your threat to the target. However, due to the 15% damage increase, it's also quite handy as a DPS increase after the tank has a sizable threat lead. By 'swapping' this with other rogues, you effectively negate the extra threat too.
Disarm:
Some bosses hit very hard. Other bosses have Adds that hit very hard. Disarming them can substantially reduce the time taken for a tank to die (Onyxia's guards with more than one with the buff for example). Other:
- Spell casting slow down (poison)
- Healing reduction (poison)
- Speed Reduction (posion)
- Interrupts
- Stun lock
- Sap
- Armor reduction

And some spec specific debuffs like Hemorrage and Savage Combat. However, I believe most of these can also be provided by other classes.

Just some notable things. I've probably forgotten some...

Note: Tricks of the Trade does something I forgot about (credit to Takkara), which is AoE threat when coupled with Fan of Knives.
Note: These are my own experiences, where rogues aren't necessarily as geared as hunters

My opinion only, but rogues are one of the most fun classes to play pve or pvp. I always like having a skilled rogue when i raid for the bosses, this is when a rogue shows its dps potential. A good rogue knows his job and doesnt worry about his dps in heroics or what buffs he doesnt bring, he goes all out on raid bosses and if he doesnt top the meter, he isnt to far behind.

Rogues can do some devastating DPS. I've seen one who was at the time worse geared than me (I was in ulduar-10 epics) do around 1000 - 1500 more DPS than me. The highest I've seen him do was around 5500 - 6000 dps.

I think the rogue is one of the few classes you need real skill for to play. If you play it right, for example, use the right finishing moves at the right times, you can do some awesome dps.